In general, pressure-sensitive adhesive (PSA) has properties to be in a soft solid (viscoelastic) state in a room temperature range and easily adhere to adherend with some pressure applied. In particular, acrylic PSA is superior in lightfastness, weatherability, oil resistance, etc., to rubber-based PSA; and therefore, PSA sheets having acrylic PSA are widely used for joining, fastening and so on in various fields. Technical literatures related to PSA sheet using acrylic PSA include Patent Documents 1 to 3.